1. Field of the Invention
The present invention generally relates to golf balls, and more particularly, to a golf ball having an improved dimple pattern.
2. Description of the Related Art
Golf balls generally include a spherical outer surface with a plurality of dimples formed therein. Conventional dimples are depressions that act to reduce drag and increase lift. These dimples are formed where a dimple wall slopes away from the outer surface of the ball, forming the depression.
Dimples typically have a circular cross sectional profile. However, dimple having profiles of other shapes are also possible. Such other profiles include parabolic curve, ellipse, semi-spherical curve, saucer-shaped curve, sine curve, truncated cone, flattened trapezoid, or the shape generated by revolving a catenary curve about its symmetrical axis. Other possible dimple designs include dimples within dimples and constant depth dimples.
Drag is the air resistance that acts on the golf ball in the direction opposite the ball""s flight direction. As the ball travels through the air, the air that surrounds the ball has different velocities and, thus, different pressures. The air exerts maximum pressure at a stagnation point on the front of the ball. The air then flows around the surface of the ball with an increased velocity and reduced pressure. At some separation point, the air separates from the surface of the ball and generates a large turbulent flow area behind the ball. This flow area, which is called the wake, has low pressure. The difference between the high pressure in front of the ball and the low pressure behind the ball slows the ball down. This is the primary source of drag for golf balls.
The dimples on the golf ball cause a thin boundary layer of air adjacent to the ball""s outer surface to flow in a turbulent manner. Thus, the thin boundary layer is called a turbulent boundary layer. The turbulence energizes the boundary layer and helps move the separation point further backward, so that the layer stays attached further along the ball""s outer surface. As a result, there is a reduction in the area of the wake, an increase in the pressure behind the ball, and a substantial reduction in drag.
Lift is an upward force on the ball that is created by a difference in pressure between the top of the ball and the bottom of the ball. This difference in pressure is created by a warp in the airflow that results from the ball""s backspin. Due to the backspin, the top of the ball moves with the airflow, which delays the air separation point to a location further backward. Conversely, the bottom of the ball moves against the airflow, which moves the separation point forward. This asymmetrical separation creates an arch in the flow pattern that requires the air that flows over the top of the ball to move faster than the air that flows along the bottom of the ball. As a result, the air above the ball is at a lower pressure than the air below the ball. This pressure difference results in the overall force, called lift, which is exerted upwardly on the ball. For additional discussion regarding golf ball aerodynamics, see copending patent application No. 09/989,191 entitled xe2x80x9cGolf Ball Dimples with a Catenary Curve Profile,xe2x80x9d filed on Nov. 21, 2001 and 09/418,003 entitled xe2x80x9cPhyllotaxis-Based Dimple Patterns,xe2x80x9d filed on Oct. 14, 1999, both of which are incorporated herein in their entireties.
By using dimples to decrease drag and increase lift, golf ball flight distances have increased. In order to optimize ball performance, it is desirable to have a large number of dimples evenly distributed around the ball. In arranging the dimples, an attempt is made to minimize the space between dimples, because such space does not improve aerodynamic performance of the ball. However, since most golf ball dimples are formed using a two-piece mold, the two pieces being mated at a parting line, most golf balls have at least one great circle which corresponds to the parting line of the molds and upon which no dimples are formed.
Attempts at concealing golf ball parting lines using unusual molds have been made. One such design uses an icosahedral dimple arrangement. See U.S. Pat. No. 5,688,193, the disclosure of which is incorporated herein by reference. This design requires substantial undercuts to accommodate the icosahedral vertices. This is undesired because undercuts increase the difficulty of removing the ball from the mold. As the size of the undercuts increases, the difficulty of removing the ball from the mold increases. U.S. Pat. No. 4,653,758 discloses a golf ball design having a staggered parting line. In this design, the real parting line is only minimally displaced from the equator.
What is needed is an improved dimple pattern for which there is no great circle that does not intersect any dimples and that does not create an excessive amount of undercut.
The present invention is directed to a golf ball dimple pattern. According to one aspect of the invention, the dimples are arranged, at least in part, according to an Archimedean pattern. The dimples may be arranged on the golf ball according to an Archimedean pattern such that there is no great circle about the golf ball that does not intersect a dimple. Preferred Archimedean patterns include a truncated octahedron, a great rhombcuboctahedron, a truncated dodecahedron, and a great rhombicosidodecahedron.
According to another aspect of the invention, the golf ball has a nonplanar parting line. The parting line may include a parallel segment parallel to the true equator of the golf ball and a plurality of diverging segments that diverge and converge relative the true equator. The parallel segment may be non-collinear with the true equator. The dimples may be arranged on the golf ball such that there is no great circle about the golf ball that does not intersect a dimple. The diverging and converging parting line segments may cooperate to form areas that diverge and converge away from the true equator. The size of this area may be designed to not fully surround the biggest dimple or to minimize any undercut.